Homocystinuria (HCU) is a rare but potentially serious inherited condition.

It means the body can't process the amino acid methionine. This causes a harmful build-up of substances in the blood and urine.

Normally, our bodies break down protein foods like meat and fish into amino acids, which arethe "building blocks" of protein. Any amino acids that aren't needed are usually broken down and removed from the body.

Babies with HCU are unable to fully break down the amino acid methionine, causing a build-up of methionine and a chemical called homocysteine. This can be harmful.

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Medically Reviewed by a doctor on 29 Nov 2016